Inclusion-complexing agent for use in isolation of xylene isomer(s) and/or ethylbenzene

ABSTRACT

A mixture of xylene isomers or a mixture of a xylene isomer(s) and ethylbenzene is brought into contact with at least one specific substituted α-cyclodextrin to form an inclusion complex(es) of the substituted α-cyclodextrin with a xylene isomer or ethylbenzene included therein, from which the xylene isomer(s) and/or ethylbenzene is then extracted to isolate, or separate, the same. Inclusion-complexing agents usable in isolation, or separation, of the xylene isomer(s) and/or ethylbenzene are substituted α-cyclodextrin in the form of α-cyclodextrin having the hydrogen atom of at least one hydroxyl group thereof substituted with at least one member selected from the group consisting of a glucosyl group, a maltosyl group, maltooligosaccharide residues, a hydroxyethyl group, a hydroxypropyl group, a methyl group, a sulfonic group, alkylenesulfonic groups, and carboxyalkyl groups.

This is a continuation-in-part of application Ser. No. 583,427, filedSep. 17, 1990, now U.S. Pat. No. 5,095,173.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for efficiently isolating, orseparating, a xylene isomer(s) and/or ethylbenzene useful as a solventand a starting material for chemical syntheses, and to an agent for usein isolation, or separation, of a xylene isomer(s) and/or ethylbenzene.Starting materials usable in the process of the present inventioninclude mixtures of at least two xylene isomers selected from amongo-xylene, m-xylene and p-xylene; and mixtures of ethylbenzene and atleast one xylene isomer selected from among those mentioned above. Thesemixtures may further contain a small amount of impurities.

2. Prior Art

Xylenes are widely used as solvents and starting materials for chemicalsyntheses of synthetic resins, synthetic fibers, and the like. Amongxylene isomers, p-xylene in particular is in great demand.

On the other hand, ethylbenzene is used as a starting material ofstyrene monomer, and the like.

Individual xylene isomers (o-isomer, m-isomer and p-isomer) are usuallyobtained from the so-called mixed xylene (o-isomer: about 20%, m-isomer:about 40%, p-isomer: about 15%, ethylbenzene: about 15%, other compoundssuch as styrene: small in amount). o-Xylene and ethylbenzene can beseparated from the mixed xylene and isolated from each other byprecision distillation wherein a difference in boiling pointtherebetween is utilized. m-Xylene and p-xylene can hardly be isolatedfrom each other by distillation because the boiling points thereof areextremely close to each other. The common processes for isolatingm-xylene and p-xylene from each other include a low-temperatureprocessing method, an adsorption method, and an MGCC method (developedby Mitsubushi Gas Chemical Company, Inc.). The low-temperatureprocessing method, in which a large difference in melting point betweenm-isomer and p-isomer is utilized, is not commonly used these daysbecause it involves a drawback of processing at as low a temperature as-70° C. and a large consumption of energy used to lower the temperature.The adsorption method, in which a zeolite molecular sieve is used as anadsorbent (UOP ISOMAR AND PAREX PROCESS developed by Universal OilProducts Co., U.S.A.), is said to provide a high yield of p-xylenehaving a purity of 99% or higher even when the mixed xylene is passedonly once through the molecular sieve. The MGCC method, in whichselective complexing of m-xylene with a mixture of hydrogen fluoride andboron trifluoride is utilized, enables pure m-xylene to be recovered ina substantial yield of 100%. Thus, the adsorption method and the MGCCmethod are both excellent ones. However, the former disadvantageouslyrequires a large amount of a solvent for use in a mobile phase, whilethe latter involves a drawback of handling hydrogen fluoride, which isan intractable substance.

In view of the above, an object of the present invention is to provide anovel and economical process for highly selectively isolating, orseparating, a xylene isomer(s) and/or ethylbenzene by using asubstituted α-cyclodextrin, developed with the aim of improving thewater solubility of α-cyclodextrin. Another object of the presentinvention is to provide an agent usable for isolation, or separation, ofa xylene isomer(s) and/or ethylbenzene.

SUMMARY OF THE INVENTION

In one aspect of the present invention, there is provided a process forisolating a xylene isomer(s) and/or ethylbenzene, comprising the step ofbringing a mixture containing at least two members selected from thegroup consisting of o-xylene, m-xylene, p-xylene, and ethylbenzene intocontact with at least one substituted α-cyclodextrin in the form ofα-cyclodextrin having the hydrogen atom of at least one hydroxyl groupthereof substituted with at least one member selected from the groupconsisting of a glucosyl group, a maltosyl group, maltooligosaccharideresidues, a hydroxyethyl group, a hydroxypropyl group, a methyl group, asulfonic group, alkylenesulfonic groups, and carboxyalkyl groups to forminclusion complexes of the substituted α-cyclodextrin with a xyleneisomer or ethylbenzene included therein in accordance with therespective formation constants thereof; and the step of extracting thexylene isomer(s) and/or ethylbenzene from the inclusion complexes.

In another aspect of the present invention, there is provided aninclusion-complexing agent for use in isolation of a xylene isomer(s)and/or ethylbenzene, which is a substituted α-cyclodextrin in the formof α-cyclodextrin having the hydrogen atom of at least one hydroxylgroup thereof substituted with at least one member selected from thegroup consisting of a glucosyl group, a maltosyl group,maltooligosaccharide residues, a hydroxyethyl group, a hydroxypropylgroup, a methyl group, a sulfonic group, alkylenesulfonic groups, andcarboxyalkyl groups.

The inclusion complex of the present invention can also be used as astarting material for chemical syntheses involving a chemical reactionsuch as a novel aqueous-phase reaction by virtue of the high solubilityof the inclusion complex in water, or introduction of a substituent intoa given position of the inclusion complex by virtue of the specificchemical structure thereof.

The inclusion complex of the present invention can also used to safelystore xylene by suppressing the volatility of xylene because xyleneisomers and ethylbenzene are not dissociated from the inclusion complexunless it is heated up to about 60° C. This is significant becausexylene is so volatile and so poisonous that it is designated as asubstance regulated by the Clean Air Act of U.S.A.

The present invention will now be described in detail.

Agents usable for isolation, or separation, of a xylene isomer(s) and/orethylbenzene according to the present invention are substitutedα-cyclodextrins in the form of α-cyclodextrin having the hydrogen atomof at least one hydroxyl group thereof substituted with at least onemember selected from the group consisting of a glucosyl group, amaltosyl group, maltooligosaccharide residues, a hydroxyethyl group, ahydroxypropyl group, a methyl group, a sulfonic group, alkylenesulfonicgroups, and carboxyalkyl groups. The term "sulfonic group" as usedherein is intended to encompass not only a group in the form of freeacid but also groups in the form of a sodium, potassium, ammonium, loweramine, ethanolamine, or like salt thereof. The same meaning as describedabove in connection with the "sulfonic group" applies to the "sulfonicmoiety" of the "alkylenesulfonic group" and the "carboxyl moiety" of the"carboxyalkyl group" as well. The number of carbon atoms in the alkylenemoiety of the alkylenesulfonic group is preferably 1 to 5. Theabove-mentioned alkylene moiety may be either linear or branched. Thenumber of carbon atomsin the carboxyalkyl group, which may be eitherlinear or branched, is preferably 1 to 6.

These substituted α-cyclodextrins provide a remarkable merit that theinclusion complexes thereof with a xylene isomer or ethylbenzene are sohigh in solubility in water, as compared with those of othercyclodextrins and their substituted derivatives, that no precipitate isformed in the course of extraction thereof to enable the operation ofextraction to be advantageously simplified. The use of simpleα-cyclodextrin not chemically modified in isolation, or separation, of axylene isomer(s) has already been disclosed in patent literature [see,for example, Japanese Patent Laid-Open No. 42,825/1977, titled "Processfor Isolating Benzene Compound Isomer(s)"]. In this case, however, aninclusion complex(es) of α-cyclodextrin with a xylene isomer is yieldedin the form of a precipitate. Accordingly, a solid-liquid separationoperation is required. This is the greatest drawback in carrying out theabove-mentioned isolation process. While the use of the above-mentionedsubstituted α-cyclodextrins, e.g., glucosyl-α-cyclodextrin andmaltosyl-α-cyclodextrin in particular, to form inclusion complexesthereof has already been utilized in the fields of foodstuffs and thelike, there are no such cases as in the present invention where theabilities of such substituted α-cyclodextrins to form inclusioncomplexes thereof have ever been utilized with a view to isolating axylene isomer(s) and/or ethylbenzene.

According to the process of the present invention, a substitutedα-cyclodextrin(s as specified in the present invention is dissolved inwater to prepare an aqueous solution thereof, to which a mixture ofxylene isomers or a mixture of a xylene isomer(s) and ethylbenzene isthen added, followed by vigorous agitation or shaking of the resultantmixture. The substituted α-cyclodextrin concentration of theabove-mentioned aqueous solution is suitably 5 to 45 wt. % based on thewater, preferably 10 to 25 wt. % based on the water. Additionallystated, the use of unsubstituted α-cyclodextrin or other suchsubstituted α-cyclodextrin as to form an inclusion complex(es thereofwith a xylene isomer or ethylbenzene which has a very low solubility inwater disadvantageously causes the inclusion complex(es) to precipitatein the course of formation thereof, or unfavorably compels the formationof the inclusion complex(es) to be effected in a very low unsubstitutedor substituted α-cyclodextrin concentration in order to avoid theprecipitation of the inclusion complex(es). By contrast, theaforementioned substituted α-cyclodextrins as specified in the presentinvention can be used without any such disadvantages.

The mixing ratio of the aqueous solution of the substitutedα-cyclodextrin(s) to the mixture of xylene isomers or the mixture of axylene isomer(s) and ethylbenzene may be such that the molar amount ofthe substituted α-cyclodextrin(s) is preferably 0.1 to 1 times as muchas the total molar amount of the xylene isomer(s) and ethylbenzene, ifpresent. The agitation or shaking may be carried out as vigorously aspossible for a few minutes to several hours. The inclusion reaction mayusually be effected in the range of ordinary temperature to about 45°C., and is preferably effected at around 25° C. After completion of thereaction with the agitation or shaking, oil-water separation of thereaction mixture is carried out according to an appropriate method,examples of which include centrifugal separation that may be continuedfor 5 to 10 minutes, and other such known methods as often used inliquid-liquid extraction to improve the separability of an oil layerfrom a water layer, e.g., a method involving addition of a salt to areaction mixture.

The separation of a xylene isomer(s) and/or ethylbenzene from theinclusion complex(es) dissolved in the water layer obtained through theoil-water separation may be effected by adding a relatively low-boilingvolatile and difficultly water-soluble organic solvent hard to includeinto the substituted α-cyclodextrin(s), such as diethyl ether, to thewater layer and shaking the resultant mixture to extract the xyleneisomer(s) and/or ethylbenzene into an organic layer. Alternatively, theaqueous solution of the inclusion complex(es) may be heated todissociate the xylene isomer(s) and/or ethylbenzene from the inclusioncomplex(es), followed by natural phase separation thereof into a waterlayer and an oil layer floating on the water layer by putting it at restand subsequent collection of the oil layer of the dissociated xyleneisomer(s) and/or ethylbenzene by means of, for example, a separatoryfunnel, or followed by extraction of the dissociated xylene isomer(s)and/or ethylbenzene with a volatile and difficultly water-solubleorganic solvent of about 50° to 100° C. in boiling point hard to includeinto the substituted α-cyclodextrin(s), such as hexane. In either case,the resultant water layer is in the form of a transparent aqueoussolution of the substituted α-cyclodextrin. The organic solvent may bevaporized from the resultant organic layer containing the xyleneisomer(s) and/or ethylbenzene extracted into the organic layer to obtainthe desired xylene isomer(s) and/or ethylbenzene.

When the isolation of a desired compound (xylene isomer or ethylbenzene)through the single procedure comprising the inclusion reaction and theextraction operation is so insufficient that the desired compoundcontains other component(s) mixed therewith in an amount unfavorable forpractical use of the isolated product, repetition of the foregoingprocedure comprising the inclusion reaction and the extraction operationwill suffice to raise the purity of the desired compound. This will bedescribed more specifically.

The abilities of xylene isomers and ethylbenzene to undergo inclusionreactions with the substituted α-cyclodextrins as specified in thepresent invention to form the corresponding inclusion complexes (inshort, formation constants of inclusion comlexes) are in the order ofp-xylene>ethylbenzene>m-xylene>o-xylene. Thus, a difference in formationconstant of inclusion complex between components of an object mixture isutilized in the process of the present invention to separate, orisolate, and purify any one(s) of the components of the object mixture.

Accordingly, the purity of, for example, p-xylene or ethylbenzene, ifnot containing p-xylene, can be raised when the procedure comprising theinclusion reaction and the extraction operation according to the presentinvention is repeated using as a starting material the residue liquidobtained by vaporizing the organic solvent from the organic layercontaining the xylene isomer(s) and/or ethylbenzene extracted thereintoand obtained using the aforementioned procedure according to the presentinvention. On the other hand, a larger amount of, for example, o-xyleneremains in the oil layer obtained through the aforementioned oil-waterseparation effected after the inclusion reaction. Accordingly, thepurity of o-xylene can be raised when the procedure comprising theinclusion reaction and the extraction operation according to the presentinvention is repeated using as a starting material the above-mentionedoil layer. In either case, the number of times required to repeat theprocedure comprising the inclusion reaction and the extraction operationaccording to the present invention to isolate one component of theobject mixture as a substantially pure substance, needless to say,depends on the initial composition of the object mixture.

The molecules of the substituted α-cyclodextrin used in the process ofthe present invention do not undergo decomposition in themselvesthroughout the foregoing whole process. Accordingly, the usedsubstituted α-cyclodextrin can be reused after recovery thereof.

The utilization of the substituted α-cyclodextrin as theinclusion-complexing agent for use in the process of the presentinvention may be applied to isolation of a component(s) of not only theso-called mixed xylene as a mixture of all xylene isomers andethylbenzene but also various mixtures including all possiblecombinations mainly composed of at least two members selected from amongthree xylene isomers (o-isomer, m-isomer and p-isomer) and ethylbenzene.

It will be possible to evolve the process of the present invention intoa liquid-liquid chromatographic process for continuously isolating thecomponents of a mixture containing a xylene isomer(s) and/orethylbenzene while using as a vehicle a substitued α-cyclodextrin(s) asspecified in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the present inventionwill be apparent to those skilled in the art from the following detaileddescription of specific embodiments, taken in connection with theaccompanying drawings in which:

FIG. 1 is a graph showing the relationship between the composition of amixture of m-xylene and p-xylene as a starting material and thecorresponding composition of an oil extract obtained through the processof the present invention in Example 6,

FIGS. 2 and 3 are NMR spectra of inclusion-complexing agents; and

FIGS. 4 and 5 are NMR spectra of the inclusion complexes of the agentsof FIGS. 2 and 3 with p-xylene.

DETAILED DESCRIPTION OF THE DRAWINGS

The details as to FIG. 1 are set forth in Example 6 hereinbelow.

FIGS. 2 to 5 are NMR spectra showing the difference between theinclusion-complexing agents per se and their inclusion complexes withp-xylene, produced and isolated in accordance with the exampleshereinbelow.

The NMR spectra were obtained as follows:

1-1) Preparation of Sample Solution of Inclusion, Complex

0.52 g of p-xylene (guaranteed reagent manufactured by Wako PureChemical Industries, Ltd.) was added to 5 ml of a 10 wt. % solution ofmonoglucosyl-α-cyclodextrin or monomaltosyl-α-cyclodextrin in heavywater. The resultant mixture was stirred at 25° C. for 10 minutes.Thereafter, the reaction mixture was subjected to 5 minutes ofcentrifugal separation at 3,000 rpm. 0.1 ml of the resultant heavy waterlayer was collected, and admixed with 0.9 ml of heavy water to prepare asample solution of an inclusion complex for NMR measurement.

1-2) Preparation of Sample Solution of Substituted α-Cyclodextrin

A sample of monoglucosyl-α-cyclodextrin or monomaltosyl-α-cyclodextrinwas dissolved in heavy water (purity: 99.75 wt. % or higher,manufactured by Wako Pure Chemical Industries, Ltd.) in such an amountas to make the sample concentration of the resultant solution about 1 %.

1-3) NMR Measurement Conditions

apparatus: JNM-FX 90Q FT NMR spectrometer (manufactured by JEOL, Ltd.)

resonance frequency: 90 MHz

measurement temperature: room temperature

solvent: D₂ O (heavy water)

internal standard: TMS (tetramethylsilane)

Note 1: TMS is not usually used because it is substantially insoluble inheavy water. In this case of NMR measurement, however, TMS could be usedwithout trouble. This is believed to be attributable to the presence ofan α-cyclodextrin derivative in the heavy water solution wherein someamount of TMS might have been dissolved.

Note 2: A strong peak at around 4.5 ppm in NMR spectra is assigned toDOH which was formed through replacement of an H atom for a D (heavyhydrogen) atom.

accumulation: 16 times

1-4) Results

In the MNR spectrum of an inclusion complex ofmonoglucosyl-α-cyclodextrin with p-xylene as well as an inclusioncomplex of monomaltosyl-α-cyclodextrin with p-xylene, two peakscharacteristic of p-xylene can be seen. A peak at 2.10 ppm is assignedto the protons of the methyl groups of p-xylene, while a peak at 6.97 isassigned to the protons of the benzene ring of p-xylene.

By contrast, such peaks are not seen in the NMR spectrum of eithermonoglucosyl-α-cyclodextrin or monomaltosyl-α-cyclodextrin.

It was confirmed that the NMR spectra of heavy water layers obtainedafter respectively shaking together with diethyl ether the heavy watersolution of the inclusion complex of monoglucosyl-α-cyclodextrin withp-xylene and the heavy water solution of the inclusion complex ofmonomaltosyl-α-cyclodextrin with p-xylene has no peaks assigned to theprotons of p-xylene. This substantiates that p-xylene was extracted fromeither of the inclusion complexes.

BEST MODES FOR CARRYING OUT THE INVENTION

The following Examples will more specifically illustrate the presentinvention, but should not be construed as limiting the scope of theinvention.

EXAMPLE 1

0.17 g of a commercially available guaranteed reagent of xylene having acomposition as listed in Table 1 was added to 5 ml of a 10 wt. % aqueoussolution of monomaltosyl-α-cyclodextrin. The resultant mixture wasstirred at 25° C. for one hour. Thereafter, the reaction mixture wassubjected to 10 minutes of centrifugal separation at 2,500 r.p.m. Theresultant water layer was separated from the organic layer, and thenadmixed with diethyl ether by shaking. The diethyl ether was vaporizedfrom the resultant ether layer to obtain an organic substance.

Table 1 shows changes in the proportions of the components of thereagent in this Example, which are the results of capillary gaschromatographic analyses. The figures in Table 1 refer to thepercentages of the components in terms of the percentage of the area ofa peak assinged to each component based on the total area of all peaks.

                  TABLE 1                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                 Starting Material                                                                        Oil Extract                                            ______________________________________                                        ethylbenzene  16.3%        18.0%                                              o-xylene      21.4%         5.0%                                              m-xylene      44.5%        15.8%                                              p-xylene      17.8%        61.2%                                              ______________________________________                                    

EXAMPLE 2

0.24 g of a mixture of xylene isomers and ethylbenzene having acomposition as listed in Table 2 was added to 5 ml of a 10 wt. % aqueoussolution of monomaltosyl-α-cyclodextrin. Thereafter, substantially thesame procedure as in Example 1 was repeated.

Table 2 shows changes in the proportions of the components of themixture in this Example. In Table 2, the figures have the same meaningas in Example 1.

                  TABLE 2                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                 Starting Material                                                                        Oil Extract                                            ______________________________________                                        ethylbenzene  24.0%        22.3%                                              o-xylene      25.9%         4.4%                                              m-xylene      25.2%         7.6%                                              p-xylene      24.9%        65.7%                                              ______________________________________                                    

0.17 g of a mixture of ethylbenzene, o-xylene and m-xylene having acomposition as listed in Table 3 was added to 5 ml of a 10 wt. % aqueoussolution of monomaltosyl-α-cyclodextrin. Thereafter, substantially thesame procedure as in Example 1 was repeated.

Table 3 shows changes in the proportions of the components of themixture in this Example. In Table 3, the figures have the same meaningas in Example 1.

                  TABLE 3                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                 Starting Material                                                                        Oil Extract                                            ______________________________________                                        ethylbenzene  32.7%        65.2%                                              o-xylene      34.1%        10.2%                                              m-xylene      33.2%        24.6%                                              ______________________________________                                    

EXAMPLE 4

0.17 g of a mixture of o-xylene and m-xylene having a composition aslisted in Table 4 was added to 5 ml of a 10 wt. % aqueous solution ofmonomaltosyl-α-cyclodextrin. Thereafter, substantially the sameprocedure as in Example 1 was repeated.

Table 4 shows changes in the proportions of the components of themixture in this Example. In Table 4, the figures have the same meaningas in Example 1.

                  TABLE 4                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                Starting Material                                                                        Oil Extract                                             ______________________________________                                        o-xylene     51.2%        27.8%                                               m-xylene     48.8%        72.2%                                               ______________________________________                                    

EXAMPLE 5

0.16 g of a mixture of o-xylene, m-xylene and p-xylene having acomposition as listed in Table 5 was added to 5 ml of a 10 wt. % aqueoussolution of monomaltosyl-α-cyclodextrin. Thereafter, substantially thesame procedure as in Example 1 was repeated.

Table 5 shows changes in the proportions of the components of themixture in this Example. In Table 5, the figures have the same meaningas in Example 1.

                  TABLE 5                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                Starting Material                                                                        Oil Extract                                             ______________________________________                                        o-xylene     33.7%        5.5%                                                m-xylene     32.2%        8.6%                                                p-xylene     34.1%        85.9%                                               ______________________________________                                    

EXAMPLE 6

0.544 g of an equimolar mixture of p-xylene and m-xylene was added to 5g of a 10 wt. % aqueous solution of monoglucosyl-α-cyclodextrin.Thereafter, substantially the same procedure as in Example 1 wasrepeated.

Using each of mixtures of p-xylene and m-xylene respectively havingvaried p-xylene proportions of 10%, 25%, 75%, 90% and 98%, substantiallythe same procedure as described above was repeated.

Table 6 shows changes in the proportions of the components of themixtures in this Example. In Table 6, the figures have the same meaningas in Example 1.

                  TABLE 6                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                Starting Material                                                                        Oil Extract                                             ______________________________________                                        m-xylene     90.0%        50.0%                                               p-xylene     10.0%        50.0%                                               m-xylene     75.0%        28.7                                                p-xylene     25.0%        71.3%                                               m-xylene     50.0%        12.5%                                               p-xylene     50.0%        87.5%                                               m-xylene     25.0%         5.8%                                               p-xylene     75.0%        94.2%                                               m-xylene     10.0%         2.1%                                               p-xylene     90.0%        97.9%                                               m-xylene      2.0%         0.0%                                               p-xylene     98.0%        100.0%                                              ______________________________________                                    

The data in Table 6 are also summarized in FIG. 1.

EXAMPLE 7

6 g of a commercially available guaranteed reagent of xylene having acomposition as listed in Table 7 were added to 10 ml of a 20 wt. %aqueous solution of monogulcosyl-α-cyclodextrin. The resultant mixturewas stirred at 25° C. for 2 hours, followed by oil-water separation. Theincluded oil components present in the resultant water layer wereextracted with diethyl ether, which was then distilled off to obtain0.10 g of an oil residue containing concentrated p-xylene. Using thisoil residue and 3 ml of a 20 wt. % aqueous solution ofmonoglucosyl-α-cyclodextrin, substantially the same procedure comprisingthe inclusion reaction and the extraction operation as described abovewas repeated.

Table 7 shows changes in the proportions of the components of thereagent in this Example. In Table 7, the figures have the same meaningas in Example 1.

                  TABLE 7                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                              Starting  First Oil                                                                              Second Oil                                                 Material  Extract  Extract                                           ______________________________________                                        ethylbenzene                                                                             17.1%       21.4%    5.3%                                          o-xylene   20.5%        2.7%      0%                                          m-xylene   43.3%       16.3%    0.4%                                          p-xylene   19.1%       59.6%    94.3%                                         ______________________________________                                    

EXAMPLE 8

3.0 g of a commercially available guaranteed reagent of xylene having acomposition as listed in Table 8 were added to 10 ml of a 20 wt. %aqueous solution of a mixture of maltosyl-α-cyclodextrins (containing asthe main ingredients 41 wt. % of monomaltosyl-α-cyclodextrin and 43 wt.% of dimaltosyl-α-cyclodextrins). The resultant mixture was stirred at25° C. for 5 minutes. Thereafter, substantially the same procedure as inExample 1 was repeated.

Table 8 shows changes in the proportions of the components of thereagent in this Example. In Table 8, the figures have the same meaningas in Example 1.

                  TABLE 8                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                                 Starting Material                                                                        Oil Extract                                            ______________________________________                                        ethylbenzene  17.1%        22.8%                                              o-xylene      20.5%         3.2%                                              m-xylene      43.3%        14.4%                                              p-xylene      19.1%        59.6%                                              ______________________________________                                    

EXAMPLE 9

2.0 g of a commercially available guaranteed reagent of xylene having acomposition as listed in Table 9 were added to 50 ml of a 20 wt. %aqueous solution of monoglucosyl-α-cyclodextrin. The resultant mixturewas stirred at 25° C. for 30 minutes, followed by oil-water separation.The resultant water layer alone was collected, and heated at 80° C. toturn turbid and subsequently transparent as a result of dissociation ofoil components from inclusion complexes. The oil components existing onthe surface of the water layer were collected and analyzed.

Table 9 shows changes in the proportions of the components of thereagent in this Example. In Table 9, the figures have the same meaningas in Example 1.

                  TABLE 9                                                         ______________________________________                                        Changes in Proportions of Components                                          through Inclusion Reaction and Extraction                                               Starting                                                                             Oil Components Dissociated                                             Material                                                                             from Water Layer                                             ______________________________________                                        ethylbenzene                                                                              17.1%    21.3%                                                    o-xylene    20.5%     1.3%                                                    m-xylene    43.3%    11.8%                                                    p-xylene    19.1%    65.6%                                                    ______________________________________                                    

According to the present invention, a component(s) of a mixture ofxylene isomers or a mixture of a xylene isomer(s) and ethylbenzene canbe highly selectively isolated, or separated, through an inclusionreaction(s) and an extraction operation(s).

A substituted α-cyclodextrin(s) after extraction therefrom of a desiredcompound(s) can be repeatedly used in the inclusion reaction(s) and theextraction operation(s). This, coupled with the simplicity of theextraction operation in the process of the present invention, can reducethe cost of isolation, or separation, of the xylene isomer(s) and/orethylbenzene.

It will be understood that the specification and examples areillustrative but not limitative of the present invention and that otherembodiments within the spirit and scope of the invention will suggestthemselves to those skilled in the art.

What is claimed is:
 1. An inclusion complex of at least one of a xyleneisomer and ethylbenzene, and of a substituted α-cyclodextrin having thehydrogen atom of at least one hydroxyl group thereof substituted with atleast one member selected from the group consisting of a glucosyl group,a maltosyl group, a maltooligosaccharide residue, a hydroxyethyl group,a hydroxylpropyl group, a methyl group, a sulfonic group, analkylenesulfonic group, and a carboxyalkyl group.
 2. An inclusioncomplex according to claim 1, wherein the hydrogen atom of the hydroxylgroup of α-cyclodextrin is substituted with at least one member selectedfrom the group consisting of a glucosyl group, a maltosyl group, amaltooligosaccharide residue, a sulfonic group, an alkylenesulfonicgroup, and a carboxyalkyl group.
 3. An inclusion complex according toclaim 1, wherein the hydrogen atom of the hydroxyl group of theα-cyclodextrin is substituted with at least one member selected fromgroup consisting of a hydroxyethyl group and a hydroxypropyl group. 4.An inclusion complex according to claim 1, wherein the hydrogen atom ofthe hydroxyl group of the α-cyclodextrin is substituted with a methylgroup.